1. Field of the Invention
The present invention relates to a chest brace and method of using a chest brace to prevent collapse of a chest wall of a patient, such as a neonate, to keep the lungs inflated. More particularly, the present invention pertains to an inexpensive chest brace that interacts with the skin covering the chest, rather than through applied negative air pressure, to provide a distending force on the chest wall to prevent its collapse, especially during respiration.
2. Description of the Related Art
Pulmonary insufficiency associated with immaturity is one of the most common life-threatening hurdles that confronts the premature newborn baby. The newborn's rib cage is soft and buckles easily during spontaneous respiration, particularly during inspiration. Underdevelopment of the intercostal muscles, lungs, or both contributes to the chest's deformability. In premature infants below 30 weeks gestation, thoracic wall elastic recoil is almost non-existent, so that the resting volume of the lungs is very close to or below their collapsed volume. Also, the relatively compliant chest wall tends to collapse as the diaphragm descends, resulting in a diminished tidal volume. As a result, most premature infants require assisted ventilation or a continuous distending pressure (CDP).
Continuous positive airway pressure (CPAP) is widely established as an effective method for preventing lung wall collapse, chest wall distortion, and for increasing oxygenation. Currently, CPAP is used almost exclusively in preference to continuous negative distending pressure. CPAP, however, is potentially hazardous to newborn infants with weakened respiratory systems. It is usually administered by nasal prongs, but has major limitations and serious side effects. These include: nasal trauma, difficulty in obtaining a good fit in very small infants, and high gas flows that cause airway cooling, drying, and obstruction of the nasal passages. During periods of crying and mouth opening, especially with high CPAP flows, there is a loss of pressure and the infant inhales room air. Frequent dislodgement of the nasal prongs makes nursing difficult, especially when associated with repeated bouts of desaturation. High or fluctuating saturation may increase the risk of retinopathy. Perhaps more serious are the circulatory disturbances, decreased venous return to the heart, diminished cardiac output, and increased intra-cranial hemorrhage.
Negative pressure applied intermittently around the chest has been used for more than a 100 years as a way of assisting ventilation in patients with respiratory failure. The iron lung is perhaps one of the best recognized negative pressure ventilators. Continuous negative distending pressure (CNP) is used to manage a number of specific conditions that produce respiratory failure in neonates and older infants. Negative distending pressure is highly effective and does not have many of the side effects of CPAP. Among its benefits with patients with respiratory disease syndrome are an increase in resting volume of the lung and arterial oxygen tension. There is also no need for an airway or nasal prongs. As opposed to positive distending pressure, CNP produces a decrease in intrathoracic and right arterial pressures, favoring venous return to the heart from parts of the body that are not exposed to the negative pressure. CNP further increases lung lymph flow and lung albumen transport. CNP also avoids the increases in pulmonary vascular resistance and pulmonary artery pressure that are observed with positive airway pressure. Recently, CNP has been re-introduced to treat infants with various pathological conditions.
While improvements have been made in the design of devices for generating extra-thoracic negative pressure, the devices are still difficult to attach to small newborns. Current designs consist of a cuirass or chamber and use vacuum around the chest or lower body to generate negative pressure. These devices require some form of electrical power supply, are relatively expensive, and are cumbersome. Technical difficulties are associated with temperature control, neck seals obstructing venous return, leaks around the seals and limited patient access. These devices also require considerable training and experience to operate and the technical problems make nursing difficult and frustrating. This limits the use of a potentially life saving treatment modality.
There are also situations where the thoracic shape of the newborn is not within normal thresholds, regardless of whether or not the chest is collapsing during respiration. A normal, healthy infant has a thoracic index between approximately 85%-95%. Thoracic index is defined as the ratio of the height of the chest, i.e., in an anterior-to-posterior direction or vice versa, over the width of the chest, i.e., in a lateral or side-to-side direction, when measured in the prone or supine position. Newborns with a thoracic index of less than 65%, for example, are generally not considered healthy. This decrease may or may not be related to collapsing of the chest during respiration. For example, a decreased thoracic index can be due to a malformation, or it may be present simply because the infant's chest has collapsed to a point at beyond which it can collapse no further. In such infants, there is a need to restore the thoracic index to its normal range. However, conventional assisted ventilation and CNP devices, which used primarily to prevent lung collapse, does little or nothing to improve the infant's thoracic index.